eLFH - Physiological changes during Pregnancy Flashcards
Usual weight gain during pregnancy
10 to 20 kg
Recommended weight gain for women with normal pre-pregnancy BMI
11.5 to 16 kg
Cause of weight gain during pregnancy
Foetal growth
Placenta
Amniotic fluid
Uterus
Breasts
Fat
Blood
Extravascular extracellular fluid
Cause of aortocaval compression
Weight of gravid uterus compress great vessels against lumbar vertebral bodies
(IVC > Aorta)
Consequence of aortocaval compression
IVC obstruction causes fall in venous return to heart leading to drop in maternal cardiac output and BP
Common alternative name for aortocaval compression
Supine hypotension
Symptoms of aortocaval compression
Dizzy
Nausea
Therefore women usually learn to avoid this position
Consequence if aortic compression predominates aortocaval compression
Maternal BP (measured above level of compression) will be normal or raised
However blood supply to uterus and fetoplacental unit (originates below level of compression) reduces and compromises foetus without maternal hypotension
Azygous venous system
Internal vertebral venous plexus around spinal cord
Consequence of IVC compression on azygous venous system
Azygous venous system becomes dilated with IVC compression
Causes engorgement of veins within the spinal canal
Degree of tilt to left side required to reliably avoid aortocaval compression
15 degrees is the compromise
Realistically need 30 degrees
Full left lateral position impractical for obstetric procedures
Gestation from which left lateral tilt is required
20 weeks onwards
Approximate uterine blood flow at term
700 ml/min
Blood supply to the uterus
Graph of changes to heart rate, stroke volume and cardiac output during pregnancy with weeks gestation
Why does cardiac output increase further during labour and by how much
CO increases by further 40% due to pain
Why does cardiac output increase immediately following delivery
Autotransfusion of blood from the uterus
Caution with autotransfusion of blood from uterus
If high risk of fluid overload then can precipitate this from point of delivery to around 48 hours after
Volume of blood autotransfused from uterus to mother as uterus contracts
~ 500 ml
Average resting heart rate during pregnancy
85 bpm
Changes to blood pressure during pregnancy
Systolic and diastolic pressure fall (diastolic more so than systolic) and then increases back to pre-pregnancy BP by term
Gestation at which BP is at its lowest
20 weeks
Cause for drop in BP during pregnancy
Fall in systemic vascular resistance
MAP = CO x SVR
Spirometry trace of non-pregnant vs pregnant adult
Lung volumes which are increased in pregnancy
Tidal volume
Respiratory rate
Minute ventilation
Lung volumes which are reduced in pregnancy
Functional residual capacity
Expiratory reserve volume
Residual volume
Total lung capacity
Why does pregnancy cause faster fall i PaO2 during apnoea
Reduced FRC
Higher oxygen demands